1. Field of the Invention
The present invention relates to a friction stir welding method for welding by use of a rotary tool having a pin portion and a shoulder portion. In addition, the present invention relates to a welded component part obtained by the friction stir welding method.
2. Description of the Prior Art
The friction stir welding method is a method wherein a pin portion of a rotary tool made of a material harder than members to be welded is inserted between abutment surfaces of the members to be welded, and frictional heat and plastic flow are caused at the abutment surfaces by rotation and movement of the rotary tool, thereby welding the members. One example of the friction stir welding method is described in Japanese Patent Laid-open No. 11-10368 (1999). Since the members to be welded can be welded at a temperature equal to the melting point or below thereof by the friction stir welding, this technique has the effects that strain after welding is little, the surfaces of the members remain aesthetically good, and so on.
The friction stir welding method is suitable for welding members which are the same or similar in physical properties or mechanical properties. However, where the members to be welded are conspicuously different in physical properties, for example, melting point or density, or where the members to be welded are conspicuously different in mechanical properties, the friction stir welding method results in that a defective weld is liable to be generated and a sound weld is difficult to obtain.